Purified hydrogen gas is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen gas also is an important fuel source for many energy-conservation devices. For example, fuel cells utilize purified hydrogen gas and an oxidant to produce an electric current. Various processes and devices may be used to produce hydrogen gas. However, many hydrogen-producing processes produce an impure hydrogen gas stream, which also may be referred to as a reformate stream and/or as a mixed gas stream that contains hydrogen gas and other gases. Prior to delivering this impure hydrogen stream to a fuel cell stack or other hydrogen-consuming device, the mixed gas stream may be purified, such as to remove at least a portion of the other gases.
Separation assemblies, which may include and/or may be referred to herein as separation regions, hydrogen purifiers, and/or as hydrogen separation assemblies, may be utilized to facilitate this purification. Such separation assemblies may include one or more hydrogen-selective membranes arranged within a membrane module. The hydrogen-selective membranes may be permeable to hydrogen gas but impermeable, or at least substantially impermeable, to the other gases. Such hydrogen-selective membranes also may be referred to herein as membranes.
The separation assembly may be configured to flow the mixed gas stream past a first, or mixed gas, face, or side, of the hydrogen-selective membranes, and the hydrogen gas may diffuse through the hydrogen-selective membranes to a second, or permeate, face, or side, of the hydrogen-selective membranes. Purified hydrogen gas then may be collected from the permeate side of the hydrogen-selective membranes. A portion of the mixed gas stream that does not diffuse through the hydrogen-selective membranes, which includes a substantial portion of the other gases, may be discharged from the separation assembly as a byproduct stream.
Hydrogen-selective membranes generally are formed from a noble metal, such as palladium, a palladium alloy, and/or a palladium-copper (Pd—Cu) alloy, and these noble metals are costly to obtain. In addition, a diffusion rate of hydrogen gas through the hydrogen-selective membranes may be proportional to a thickness of, or a distance that the hydrogen gas must diffuse through, the hydrogen-selective membranes. As such, it may be desirable to decrease a thickness of the hydrogen-selective membranes and/or to utilize hydrogen-selective membranes that are very thin, with conventional hydrogen-selective membranes generally having a thickness of 15-25 microns.
Utilizing a thinner hydrogen-selective membrane increases a volume of hydrogen gas that may be separated for a given pressure differential across the hydrogen-selective membrane and for a fixed concentration of hydrogen gas on the mixed gas face of the hydrogen-selective membrane. This, in turn, permits a reduction in the total area of hydrogen-selective membrane needed to obtain a desired, target, or designed, flow rate, or volume, of hydrogen gas from separation assemblies that utilize hydrogen-selective membranes. Thus, thinner membranes decrease a total mass, or volume, of noble metal needed to obtain the desired flow rate of hydrogen gas from the separation assembly, thereby decreasing an overall cost of the separation assembly.
While Pd—Cu hydrogen-selective membranes thinner than 15 microns exist, they may be challenging to incorporate into membrane-based hydrogen separation assemblies due to the fragility of the membranes. This difficulty may be due to the likelihood of irreversible mechanical damage to the thin membrane, which may be caused by a membrane support that supports the membrane during use and/or thermal cycling of the separation assembly, and/or by mechanical loading of components in the separation assembly. Various membrane supports have been utilized for supporting thinner membranes in the hydrogen separation devices, but they have been proven to be cost-prohibitive and/or difficult to implement. Thus, there exists a need for improved membrane modules for hydrogen separation.